The field of the invention is electric motors for photographic cameras and the present invention is particularly related to an attachable electric motor for photographic cameras which drives the shutter and the film transport.
Attachable motors for use in photographic cameras are known in many embodiments. Two large groups may be distinguished. The first is one in which the motor is functionally connected with the camera shutter so that prior to the end of the shutter motion the shutter emits a signal to the motor to control the motor's action. This certainly requires an electric connection between the camera and the attached motor in the form of electrical contacts. Beside the costliness of such motors, these connecting contacts form a constant--at least a potential--source of malfunction because they are always exposed to the danger of oxidation. Furthermore, the camera and the motor require a common design so as to ensure that the contacts will match. This means that existing cameras ordinarily cannot be retro-fitted with such motors.
In the second group of attachable motors, there is no such connection between the camera shutter and the motor. Most of the time such motors are of simple design and are characterized further by their typically easy adaptation to extant cameras. No more is required to that end than making a connection at the bottom of the camera between the motor output shaft and that shaft of the camera which ordinarily is actuated by the film-transport and shutter rewind lever. This connection may be a simple mechanical plug-in connection which merely ensures that the manual force otherwise transmitted from the camera rewind lever to the shaft is now transmitted from the motor to the shaft.
However, this second group of embodiments suffers from a significant drawback. Because of the lack of functional connection between the camera shutter and the motor, the motor also fails to receive a signal from the shutter when the end of the shutter sequence has come and when the time comes for the motor to begin winding up the shutter and transporting the film. The possibility of manufacturing a camera motor in simple and economical manner allowing adaptation to extant cameras is balanced in the second group of embodiments against accepting the drawback of making the motor run according to a virtually frozen plan at a time previously frozen by design and following the shutter release. Thus as regards a known motor previously used in practice, the design required that 1/30 of a second following shutter release, the motor began winding up the shutter again and transporting the film. This means that the motor satisfactorily operates only within the shorter time interval, that is for instance between 1/1000 and 1/30 of a second in which the shutter had already gone through its sequence by the time the motor started running. But if the selected exposure exceeded 1/30 of a second, the motor begins running before the shutter has gone through its cycle. This leads to gear jamming and frequently to damage to the motor.
In any event, significant repairs were required to make the motor operational again. Attempts were made to eliminate such malfunctions by expressly stating in the instructions for use that no exposure times exceeding 1/30 of a second were to be used if the motor were attached.
Quite aside from the circumstance that there always were users attempting to photograph at longer exposures in spite of the instructions and hence were jamming the motor drives, it was naturally unsatisfactory that the motor would not allow photographing at longer exposures than 1/30 of a second.